Lowered Suspension Alignment

[Peter Rossato <rossato@xxxxxxxxxxxxx>]

Discussing suspension settings among car nuts has a lot of similarities
to discussing politics or religion.  Lots of firm believers in one or
another approach, none of which is entirely wrong.  So since I just
renewed all major suspension elements of my '94 325is, I have an
alignment rack appointment for Friday and need some assistance.  For the
record:  the car was already lowered with Eibach Pro Kit springs and
Bilstein Sports.  I installed new front and rear Bilstein Sports, new
front control arms (stock), new front control arm bushings (stock), new
tie rods, new front upper strut mounts ('94 M3), new rear upper mounts
('94 M3).

Having poked around the suspension for two weekends solid I have gained
an understanding of its workings and that leads to some questions.
Let's start with a comparison of M3 and stock E36 settings.

Alignment Settings (source Bentley's E36 manual)

     Front Camber
     Stock = 0 deg 58' +/- 30'    M3 = 0 deg 55' +/- 30'
     Front Caster
     Stock = 3 deg 50' +/- 30'   M3 = 6 deg 38' +/- 30'
     Front Toe
     Stock = 0 deg 18' +/- 8'     M3 = 0 deg 10' +/- 5'

     Rear Camber
     Stock = 2 deg 00' +/- 15'   M3 = 1 deg 45' +/- 10'
     Rear Toe
     Stock = 0 deg 24' +/- 6'     M3 = 0 deg 30' +/- 6'

The only major difference lies in the caster angle (set by the upper
mount strut which places the strut center line farther back than
stock).  Nominal front camber is off by 3 minutes, nominal front toe by
8 minutes.  In the rear the differences are 15 minutes for camber and 6
minutes for toe.  In most cases the difference is within the tolerance
bands.

I know a few minutes of arc seem small but can make a big difference.
But since only front toe is readily adjustable while front and rear
camber and caster can only be affected by changing the geometry of the
strut mounts (which I did) or control arms (which I didn't) it seems to
me that what I should ask the shop to do is set the toe at either the
stock or M3 settings.  The M3 setting would provide a bit better turn
in, I think.  All other settings will be what they will be based on
component geometry.  I think camber and caster should be measured and
only if there are big differences left to right should any further
action be considered.  Options, opinions, disagreements?  I appreciate
all inputs.

Of course this raises the real question that if we can only adjust front
toe without a major tear down or frame bending, why do we routinely pay
hundreds of dollars for a "four wheel alignment"?  We are only getting a
front wheel alignment and a rear wheel check.  Sounds like a scam.

Peter Rossato
'94 325is "VDERZEN"
BMW CCA National Capital Chapter

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